1. Field of the Invention
This invention relates to an exposure control device of an electronic still video camera using an image sensor such as a CCD or the like.
2. Description of the Related Art
An electronic still video camera which is arranged to record one field or one frame portion of a still image signal on a magnetic disc or the like by means of an image sensor such as a CCD has been known. In the electronic still video camera of the kind having the above stated image sensor, however, it has been difficult to expose the image sensor to an apposite amount of light either due to a difference in sensitivity characteristic between a light measuring element which is provided for obtaining exposure information and the image sensor which is provided for sensing the image of an object or due to the narrowness of the dynamic range of the image sensor.
To solve the above stated problem, a method has been proposed, for example, as disclosed in Japanese Patent Application Laid-Open No. SHO 59-104867 or SHO 60-32484. In accordance with this method, a preliminary shot is first tentatively performed with the image sensor according to the exposure conditions obtained by the light measuring element, and then conditions for a real exposure are computed on the basis of an image signal obtained by the image sensor.
However, although an apposite degree of exposure is obtainable by this method, it necessitates a complex arrangement for a shutter operation. More specifically, at least a part of the shutter must be left open for the preliminary exposure in carrying out the light re-measurement prior to the real exposure. This also necessitates a considerable length of time before a picture is obtained after the shutter release operation on the camera. In the case of a continuous shooting mode, therefore, the shooting speed lowers. Further, the necessity of the preliminary exposure for every light re-measuring action requires an additional shutter charging energy, which is a great disadvantage for a compact camera having a limited power source capacity.
Besides, in the event of continuous shooting, the prior art method which requires readjustment of the the exposure condition for every shot, as mentioned in the foregoing, results in a prolonged interval between one shot and another.